"Cathy Weeks" ) writes:
FWIW it's *generally* only reversable for a relatively short period of
time. Eventually the man's body makes antibodies against the sperm and
kills it, and when the antibody production starts it doesn't stop, and
even if it's reversed, his own body still produces the antibodies, and
kills off the sperm before it can leave his body.

I'm not sure if this is true, but I've also read that
the man can suffer autoimmune diseases. After he begins
to make antibodies against his own sperm, sometimes the
antibodies attack other parts of his body.